Vibration-damping arrangement

ABSTRACT

A vibration-damping arrangement intended to be placed in a slot-like shaft or trench in earth layers, or in water masses, wherein the arrangement includes a flexible container ( 1 ) which is pressurised by a gas in its operative state, and wherein the container has an associated gas generating device ( 2 ) which is adapted to generate a predetermined gas volume in the container at a given time delay. The vibration-damping arrangement can be used to reflect the propagation of vibrations or to restrict the occurrence of the quicksand phenomenon in water-containing ground in the event of cyclic pressure variations, e.g. in earthquake or landslip conditions. The arrangement can be conveniently combined with means for draining water from the ground in the near proximity of the container.

The present invention relates to a vibration-damping arrangement of thekind defined in the preamble of claim 1, and also to the use of such anarrangement.

It is known that the propagation of ground vibrations, for examplevibrations originating from a railroad, can be prevented, and thus alsosubsequent damage to nearby buildings for instance, by providing avertical slot-like trench or shaft in the ground down to an appropriatedepth, for instance a depth of 10 metres, wherein the extension surfaceof the slot-like shaft or ditch is orientated at right angles to thedirection between the vibration source and those installations to beprotected against vibrations. There can be inserted into such a shaft acontainer that has generally the same extensional measurements as theshaft and that includes flexible walls. The container is convenientlypressurised with a gas so that it is capable of supporting the shaftwalls. The pressurised gas in the container dampens or refracts soundtransmission. Variants of this technique allow the container to includecellular plastic bodies or the like in addition to a pressurised gas.The container-formed screen can be cast firmly in place in the shaft,for instance by filling the shaft with a hardenable or a curable liquidmass, into which the container is submerged and the mass then allowed toharden.

The submersion of the vibration-damping screen into such a liquid-likemass in a slot-like shaft can be facilitated by mounting/fastening amajor surface of the container to a plate, for instance a concrete plateof the same size and area as the container. Alternatively, thevibration-damping screen can be fitted to a frame structure thatfacilitates submersion of the screen in the liquid-like mass against theaction of the buoyancy forces of the screen/container in said castingmass. Another alternative in this regard involves connecting the loweredge of the screen container to a heavy horizontal bar whose mass issufficiently great to draw the gas-filled container into the liquid massin the shaft. It is, of course, conceivable to first insert thescreen-forming container into the shaft in an inflated and sealed state,and then introduce the liquid hardenable mass into the shaft.

Alternatively, the screen may, of course, be placed in the shaft andanchored therein in a non-inflated/non-pressurised state and theninflated/pressurised in the presence of or in the absence of a flowablehardenable mass.

However, the flexible vibration-damping screen is subjected to highinternal gas pressures in its operative state, and the container isexpected to remain sealed over a long period of time under the influenceof the vibrations whose propagation shall be refracted or absorbed bythe screen.

Consequently, high demands are placed on the impermeability of thecontainer. A screening container of this kind is usually manufacturedfrom thin plastic sheeting, metallised sheeting or plastic sheetinglaminates of a flexible nature and of high mechanical strength, highimpermeability and that can be welded effectively. The weld seams are,of course, critical and are preferably welded at the plant producingsaid containers, with no part being produced in the field itself.

Accordingly, conventional vibration-damping screens of this particulartype have been delivered from a plant in a ready-welded sealed statedand pressurised with a gas filling that is adapted to the application inquestion. Alternatively, the damping screen may be provided withinflation valves for inflation of the container in the location in whichit shall be used, whereafter the valves are closed or the container issealed-off prior to finally placing the device in its position of use,either in the ground or in a water mass.

The transportation of inflated containers from the factory to theirplace of use is expensive and problematic with respect to handling ofthe containers. Transportation also involves damage risks. Furthermore,the possibility of then lowering the screening container into the shaftor trench when the container is empty of gas is, of course, excluded inpractice.

Accordingly, one object of the present invention is to provide aflexible container intended to form a vibration-damping or vibrationreflecting screen in water or earth layers, where said container isproduced in the absence of pressurising gas so that it can betransported in a non-inflated state, for example in a rolled-up state ora coiled state, to the location in which the screening container shallbe installed, and where said container can be pressurised non-invasivelywith a predetermined gas volume prior to, during or subsequent toinserting the container into said shaft/place of use.

This object is achieved either completely or partially by means of thepresent invention.

The invention is defined in the accompanying independent Claim.

Further embodiments of the invention will be apparent from theaccompanying dependent Claims.

The invention is based on the concept of placing a gas-generating devicein the container in conjunction with the manufacture and permanentsealing of said container. The gas-generating device is of a kind thatcan be activated without penetrating the container wall. For example,according to one simple embodiment of the invention, the gas generatingdevice may include a sealed plastic film cushion that is divided intotwo spaces which are mutually separated by a membrane that can beruptured by applying an external force mechanically via the containerwall and the walls of said cushion. The spaces provided in the cushionmay include respective suitable chemical substances which when broughttogether generate a pre-chosen gas volume, wherewith the gas thusgenerated ruptures the cushion packing so as to allow the gas to beemptied into the container and pressurise said container to apredetermined extent that depends on the nature of the chemicalsubstances involved and the amounts in which they are present. Inanother embodiment, a container made, for instance, of heat insulatingmaterial is filled with gas in a solid or liquid state and then placedin the cushion. The purpose of the heat insulating material is to delaythe transition of the gas from a solid state to a gaseous state. ncertain cases, the heat insulating material may be surrounded by agas-tight container that may be provided with valve means or closuremeans that can either be opened by remote control or may be adapted tobe opened automatically by the gas pressure when said pressure reaches agiven level. This enables a pre-chosen volume of gas (in liquid or solidstate) to be metered in a simple and convenient fashion, while providingsufficient time for effective closure of the container of thegas-generating device, since the loss of gas during closure of saidcontainer is practically negligible. Moreover, there is obtained aselectable time period for placing the gas-generating device in positionbefore inflating the container arrangement.

There are, of course, other alternative embodiments of thegas-generating device. For example, the device may include a pressurisedcontainer comprised of suitable material (a gas tank, gas flask) thatcan be opened from outside the wall of the closed container, withoutpenetrating said wall. The gas-generating device may, of course, beactivated by mechanical action, by heating said device or by remotecontrol, for instance by wireless actuation, such as via radio waves andwith a selected time delay with regard to gas development in relation tothe time of actuation.

The present invention enables the flexible container for thevibration-damping screen to be manufactured in a permanently sealedstate in the absence of any substantial internal free gas volume, sothat the container will require only a small storage and transportationspace and so that the container can be folded together or coiled into atransport-friendly and handling-friendly form with regard to itstransportation to the location at which the container shall form thevibration-damping screen, by virtue of its flexible wall material. Theinvented container can be inflated at its place of use, by activatingthe gas generating device before or after inserting the container intothe slit-like shaft or trench, either before or after optional fillingof the shaft with a floatable, hardenable mass. The container may becarried by a structure that keeps the container in an outwardlytensioned state. Alternatively, the container may be coupled to a heavybody, for instance at the bottom edge surface of the container, so as tohold down the container in its inflated state in a liquid non-hardenedmass.

In one preferred embodiment of the invention, an inventive container ismounted on at least one side of a concrete structure, such as a concreteplate, having essentially the same area as the container, to enable thecontainer to be readily inserted into the slot-like shaft or trench andheld therein in connection with bringing the vibration-damping screeninto its final position.

Thin plastic sheeting that can be used for the manufacture of ascreening container arrangement according to the invention consists of alaminate or metallised foil of the kind typically used for vacuumpackaging in the food industry.

An application of the present invention is found within earthquaketechnology, to reduce or to eliminate the effect of cyclic loading inwater-saturated sand. In the case of cyclic loading of water-saturatedsand there occurs a pore water pressure that promotes the quicksandphenomenon (liquefaction). The water-saturated sand gradually looses itsstrength, which can result in significant reduction in the bearingcapacity of foundations and piles, or trigger a slope failures. It iswell known that the build-up of pore water overpressure is alreadyreduced by small gas quantities (less than 1%) in a water-saturatedsand. This effect can be achieved by installing gas-filled flexiblecontainers (cushions) in an earth layer beneath the groundwater surface.When the earth layer is subjected to cyclic loading, the pore wateroverpressure is compensated for by a reduction in the volume of gas inthe cushions (the cushions are compressed), as in the case of a shockabsorber. The volume of the cushions increases when the earthquake orlandslip has ceased and the pore water pressure diminishes.

In the case of this use application, cylindrical or spherical containers(cushions) are installed in shafts narrow trenches or predrilled holes.The shaft or the drill hole may be filled with suitablecontainer-protecting material. When the containers are buried in theground, the effect afforded by the containers can be enhanced bycombining the containers with draining means. In certain cases, it maybe meaningful to fasten the cushions to prefabricated elements (piles orplates) that may include or be provided with draining means whichfunction to reduce the amount of ground water present in the closevicinity of the containers, in a known manner.

In a further embodiment, vibration-damping devices are installed inwater masses to reduce the propagation of shock waves. The technologyapplied is similar to that employed in the case of ground-installedinsulating screens, although with the screen anchored either to a wallor to some other installation to be protected against the influence ofvibrations.

The invention will now be described by way of example with reference tothe accompanying drawings, in which

FIG. 1 is a schematic illustration of a container constructed inaccordance with the invention;

FIG. 2 is a schematic sectional view taken on the line II-II in FIG. 1(See the mistake in FIG. 1);

FIG. 3 is a sectional view of a ground-installed slot-like shaft inwhich an inventive container has been inserted, said container beingmounted on a supporting structure and cast in a hardened mass in theshaft;

FIG. 4 is a view taken on the line IV-IV in FIG. 3;

FIG. 5 is a variant in a reproduction corresponding to FIG. 2; and

FIG. 6 illustrates a further variant in a reproduction corresponding toFIG. 2.

FIG. 1 illustrates a generally parallelepipedic, sealingly closedcontainer 1, which is formed by the sealed connection of flexiblegas-impervious foil sheets. The container 1 has height and widthdimensions A, B in the order of metres, and a thickness or diametricaldimension C in the order of decimetres.

The container may be produced by laying two sheets of foil material onone another and joining said sheets together with a weld seam. Thecontainer 1 is essentially empty when in a closed state, with theexception of a gas generating device 2 enclosed in the container 1,wherewith the container can be rolled up, folded up, etc., to facilitatetransportation of the container from its place of manufacture to itsplace of use. It will be seen from FIG. 2 that according to oneembodiment of the gas generating device 2 the device includes a closedplastic foil cushion 21 of significantly smaller volume than the volumeof the container 1. The cushion 21 is divided by a membrane 22 into twospaces 23, 24 which contain respectively a first chemical substance(e.g. an acid) 25 and a second chemical substance (e.g. a salt) 26. Themembrane 22 can be caused to burst, by applying external forces Fagainst the cushion 21 via the container walls. As a result, the firstchemical substance will come into contact with the second chemicalsubstance and therewith generate gas in the cushion 21, which isgradually burst by the established gas pressure so that gas will flowout into the interior of the container 1 and therewith fill the same.The volume of gas generated can be predetermined by appropriate dosingof the chemical substances, so that the container 1 will be given apredetermined gas filling that is well adapted to the use conditions.

The container 1 may be conveniently mounted on a supporting structure,for instance on a concrete slab 3, having the same area as the mainsurfaces of the container 1, for insertion into a slot-like shaft ornarrow trench formed in the ground 5. The supporting structure 3, whichis shown to have a container 1 on each main surface thereof, can belowered into a can be caused to harden. It can be assumed that thecontainers 1 are pressurised with a predetermined gas volume, eitherbefore or after positioning the supporting structure 3 in the shaft ortrench 4. The shaft or trench 4 may have a depth of 10 m, for instance.The liquid mass 6 exerts pressure against the containers 1, wherein themagnitude of said pressure depends on the depth and the density of themass 6. The mass 6 hardens in its state of pressure equilibrium. Thepressurised gas in the containers 2 provides effectivescreening/dampening of vibrations that propagate generally in thedirection x and can be assumed to propagate in a direction normal to theextensional plane of the containers 1./?/

FIG. 4 illustrates a series of structures 3 with containers 1 cast inthe mass b in a slot-like shaft or trench 4 formed in the ground.

In areas where there is a risk of earthquakes, the concrete sheet orslab 3 can be replaced by a column-like element (pile or drain) and thecontainer 1 can be installed directly in a slot 4 or a drill hole. Insome cases, the liquid mass b may be replaced with drainage material.

FIG. 5 illustrates an alternative gas generating device 2 which mayinclude a pressure gas vessel 121 having an emptying valve 122 which canbe opened with the aid of a drive element 123 that can be activated by areceiver 124 capable of receiving a signal from an externally locatedoperator-controllable transmitter 125.

FIG. 6 illustrates a further alternative gas generating device 2 thatmay include gas in a liquid or a solid state 126. In certain cases, thegas can be placed in a heat insulating casing 127 which may surround agas-tight vessel 128 or which may itself form a gas-tight vessel 128.The gas-tight vessel 128 may include valve means 129 where the valve istriggered at a chosen overpressure to allow the gas to fill thecontainer 1. The heat insulation 127 enables dosing of the liquid orsolid gas volume to be readily achieved in a convenient fashion and alsoto retain the dosage of cooled liquid or solid gas to be retained over arelatively long period of time sufficient to enable the casing 127 witha possible vessel 128 to be inserted into the container 1 with a goodmargin, before any significant amount of gas has time to leave thecasing 127 or the vessel 128. Moreover, the heat insulation 127 or apossible valve means 129 can be chosen to delay the actual inflation ofthe container 1 for a selected period of time, so as to providesufficient time for comfortable transportation of a selected period oftime, so as to provide sufficient time for comfortable transportation ofthe container 1 and its insertion into its position of use prior toinflating the container 1 with said gas. The valve means 129 may beopened by remote control.

The gas-generating device may, of course, include known means fordelaying gas generation subsequent to triggering the gas-generatingdevice.

1. A vibration-damping arrangement for ground or water installation,wherein the arrangement includes a flexible container (1) which is gasinflated in an operative state and in its position of use, characterisedin that the container (1) includes an associated gas generating device(2) which is adapted to delay the delivery of gas to the container. 2.An arrangement according to claim 1, characterised in that the gasgenerating device (2) is adapted to slowly release the gas in thecontainer (1) so as to enable the closed container including said gasdelivering and gas generating device to be placed in an essentiallynon-inflated state in its place of use in which the gas generatingdevice fully inflates the container.
 3. An arrangement according toclaim 1 characterised in that the gas generating device (2) contains avolume of gas in liquid or solid, preferably cooled, state, wherein thecontainer (1) includes a gas inlet opening that can be closed,preferably by welding, subsequent to the introduction of a gas volumeinto the container, wherein the transition of the gas volume to a gasphase requires a predeterminable time period.
 4. An arrangementaccording to claim 1, characterised in that the container (1) issupported by a structure (3) with which the container (2) can be mountedin a ground-formed shaft or in a water mass.
 5. An arrangement accordingto claim 4, characterised in that the structure (3) is adapted to drainwater from the ground in the close vicinity of the container.
 6. Anarrangement according to claim 4 characterised in that the container (2)is surrounded by ground-installed drainage material.
 7. An arrangementaccording to claim 1, characterised in that the structure (3) has a masswhich prevents the structure-connected inflated container from floatingup from liquid present in a ground-formed shaft in which the containerand the structure are placed.
 8. An arrangement according to claim 7characterised in that the structure (3) is sheet-like and keeps thecontainer extended and is placed in a slot-like shaft to form avibration-damping screen.
 9. An arrangement according to claim 8,characterised in that the liquid in said shaft is a hardening mass; andin that a container (1) is placed on each side of the sheet-likestructure (3).
 10. An arrangement according to claim 3, characterised inthat the liquid or solid gas volume is encased by heat insulation thatdelays the transition of said gas volume to a gas phase.
 11. Anarrangement according to claim 1 characterised in that the gasgenerating device (2) as connected to the closed container (1) isadapted for activation at a freely selective time point.
 12. Anarrangement according to claim 1, characterised by draining means fordraining water present in the ground in the proximity of the container(1).
 13. The use of an arrangement according claim 1 for reducing thequicksand phenomenon in water-containing ground/soil in the case ofcyclic pressure variations in the ground, for instance as a result ofearthquakes.